The invention relates to improvements in apparatus for filtering plasticized materials in extruding, injection molding and like machines.
Commonly owned copending patent application Ser. No 07/446,557 of Stude et al. now U.S. Pat. No. 5,004,414 discloses a filtering apparatus wherein a housing has an inlet, an outlet and two passages each of which extends between the inlet and the outlet and receives a cylindrical filter carrier mounted for reciprocatory movement between first and second positions. When in their first positions, the carriers permit plasticized material to flow from the inlet, through filters in their filter chambers, and thence into the outlet of the housing. If one of the carriers is moved to the second position while the other carrier remains in the first position, plasticized material which has been cleaned by passing through the filter of the other carrier is diverted in part into channels leading to the filter chamber of the one carrier, and the diverted material flows counter to the normal direction of flow of plasticized material through the chamber of the one carrier to entrain intercepted impurities by way of a channel which is provided in the housing and is sealed from the chamber of the one carrier when the latter is maintained in the first position. An advantage of the filtering apparatus of Stude et al. is that the channels which serve to establish paths for the flow of filtered plasticized material counter to the normal direction of flow (toward the outlet of the housing) are always filled with flowing plasticized material when the respective filter carriers are maintained in their first positions. This is desirable and advantageous because accumulations of stagnant plastic material in the housing and/or in the filter carriers would be likely to harden and to prevent any, or to prevent predictable, flushing of impurities from the chambers of the filter carriers. The arrangement is such that, when one of the filter carriers is moved to the second position, filtered plastic material which has passed through the chamber of the other filter carrier (while the other filter carrier is maintained in the first position) flows into the chamber of the one carrier at the downstream (clean) side of the respective filter and adjacent a marginal portion of the filter to leave the chamber at the other (contaminated) side of the filter adjacent another marginal portion of the filter. Such mode of establishing a path for the flow of filtered plastic material through the chamber of the filter carrier in the second position cannot invariably ensure the expulsion of all impurities from the chambers of filter carriers and out of the housing of the filtering apparatus.
Other types of filtering apparatus are disclosed in commonly owned U.S. Pats. Nos. 4,701,118 (granted Oct. 20, 1987) to Koching et al.) and 4,725,215 (granted Feb. 16, 1988 to Kreyenborg et al.). The patent to Koching et al. discloses an apparatus wherein each reciprocable carrier supports two filters one of which is accessible when the other is in use and vice versa. The patent to Kreyenborg et al. discloses an apparatus with an exchangeable cylindrical filter holder which is reciprocable in a housing and contains a substantially plate-like filter disposed suhstantially diametrically of the holder.
German Auslegeschrift No. 1 097 660 of Corbett discloses an apparatus wherein a cylindrical filter is mounted for angular movement in a housing which is provided with an inlet for unfiltered plastic material and an outlet for filtered plastic material.
German Auslegeschrift No. 2 111 545 of Lambertus discloses an apparatus wherein a plate-like carrier supports several axially parallel filters. The carrier is movable between a plurality of positions in each of which a different set of filters can receive plasticized material from an extruder.